1. Field of the Invention
This invention relates to a high-pressure pipe string for the continuous fusion drilling of deep wells. It relates further to a process for the assembly of this high-pressure pipe string, for propelling it in the boring and for dismantling it. This invention also relates to an apparatus for the execution of the afore-mentionned processes.
Continuous fusion drilling is a drilling method in which extremely high temperatures are generated at or slightly ahead of the boring head, leading to the melting of the rock. The rock melt is evacuated into the surrounding, thermofractured (fractured by local thermal stresses) rock formation by high, locally applied pressure. The boring head can, as a result, be continuously propelled forward, melting the rock ahead of it and pushing the melt out into the surrounding cracks.
2. Description of Prior Art
Two continuous fusion drilling techniques are described in the German patent specification DE25 54 101 C2 and in the German patent disclosure 37 01 676 A1. The temperatures required to melt the rock are generated by high-pressure, hydrogen/oxygen flame jets. The process according to the German patent specification DE25 54 101 C2 is designed to effectuate a total evacuation, by high applied pressure, of the rock melt into the surrounding rock. The process according to the German patent disclosure 37 01 676 A1, on the other hand, is a profiling fusion drilling process in which only a minimal, outer profile of the boring is melted and removed, to provide a passage for the drilling device and the supply lines. The resulting melt from this area is pushed into the drilling core. After a partial cooling, the core segments are sheared off and removed to the surface. Both fusion drilling processes are designed to operate in a continuous fashion, i.e. the deep well is completed in a single, continuous thrust. The cooled melt forms a casing for the bore hole, thus providing a guide channel for the fusion drilling device and preventing cave-ins of the boring walls. The bore head can be designed for a specified service life, so that deep wells up 10,000-15,000 meters can be realized in a single, continuous process, without any time and energy-consuming "round trips."
Reliable processes must be chosen to prevent technical problems leading to interruptions of the fusion drilling process. This means processes that incorporate a minimal number of possible sources of problems, and with a sufficient redundancy in the operational systems so that a replacement unit can immediately take up the functions of any defective part of the system. A continuous drilling process significantly raises the boring velocity and can thus drastically reduce the costs of realizing a deep well. These advantages are intrinsic qualities of the fusion drilling process, which eliminates the need for the "round trips" to change the bore head and the boring rods or pipes or to remove the core, which characterizes conventional, mechanical boring methods. These advantages can, however, only be exploited if the power supply to and control of the bore head can also be performed in a continuous manner. A continuous supply of hydrogen, oxygen and cooling water at a pressure of about 2,000 bars and a vertical, mechanical driving force to the bore head are required for the realization of continuously fusion-drilled deep wells. The risk of leaks or ruptures in the joints and the possibility of signal interruptions in control wiring connectors practically exclude a segmental assembly of the high-pressure hydrogen, oxygen and cooling water supply lines. Other means must therefore be provided to carry out the continuous power supply and uninterrupted control of the bore head. These means must allow the forward motion and retrieval of the pipe string with all its supply lines and its control equipment.